United States Phone Numbers: Format, Area Code & Validation Guide

Implement Missouri phone number validation in your applications. Learn the North American Numbering Plan (NANP) format, validate exchange codes, integrate E911 emergency services, and handle number portability for Missouri's 9 area codes.

Quick Reference

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Missouri Area Codes

Missouri utilizes 9 area codes serving different regions of the state. Understanding these area codes is essential for proper number validation and routing.

Active Area Codes (as of 2025)

Key Points:

• 816 is Missouri's most populated area code, serving approximately 1.3 million of the state's 6.2 million residents
• 314 and 816 are original NANP area codes from 1947
• 235, 557, and 975 are overlay area codes that share geographic regions with existing codes
• Overlay implementations require mandatory 10-digit dialing for all calls

Sources: Wikipedia List of Missouri Area Codes, AllAreaCodes.com, Missouri Public Service Commission (verified October 2025)

Number Format Implementation Guide

Implement phone number formatting and validation in your application using these NANP structure rules and code examples.

Understanding the NANP Structure

Missouri phone numbers follow the North American Numbering Plan (NANP), established in 1947. This standardized system ensures consistent formatting and call routing across North America and the Caribbean.

Use this basic NANP format in your validation logic:

Format: +1 (NXX) NXX-XXXX
Where:
+1: Country code for the United States and Canada
N: Any digit from 2 to 9
X: Any digit from 0 to 9

These N and X digit rules prevent invalid number combinations and ensure efficient call routing.

Exchange Code Implementation Rules

Implement these exchange code rules in your validation logic. The exchange code (NXX) is the three digits immediately following the area code.

Required Rules:

• First Digit Restriction: Require the first digit (N) to be between 2 and 9. This prevents conflicts with special service codes and operator assistance.
• Second and Third Digit Flexibility: Allow any digit from 0 to 9 for the second and third digits (X).
• Restricted Combinations: Block N11 codes (211, 411, 911, etc.) reserved for specific services. Exclude these combinations in your validation logic.

Implement exchange code validation with this JavaScript function:

// Exchange code validation
function validateExchangeCode(code) {
    // First digit must be 2-9
    const firstDigit = parseInt(code[0]);
    if (firstDigit < 2 || firstDigit > 9) return false;
    
    // Check for N11 patterns (reserved service codes)
    if (code[1] === '1' && code[2] === '1') return false;

    // Note: The 555 exchange is valid for real numbers (e.g., 555-1212 for directory assistance)
    // Only 555-01XX numbers (555-0100 through 555-0199) are reserved for fictional use
    // Do not block all 555 exchange codes in production
    
    return true;
}

// Example usage:
console.log(validateExchangeCode("314")); // Returns true
console.log(validateExchangeCode("111")); // Returns false (N11 pattern)
console.log(validateExchangeCode("011")); // Returns false (first digit must be 2-9)

Test your validation logic with various valid and invalid exchange codes to ensure accuracy.

Emergency Services Implementation

Integrate E911 emergency services into your application following FCC regulations. Implement Kari's Law direct dialing, RAY BAUM's Act dispatchable location, and MLTS notification systems.

E911 Compliance Framework

Implementing E911 involves several crucial steps and regulatory compliance deadlines:

Regulatory Compliance Dates:

• Kari's Law: Effective February 16, 2020 (for MLTS manufactured, imported, offered for first sale/lease, first sold/leased, or installed after this date)
• RAY BAUM's Act Dispatchable Location:
  • January 6, 2021: On-premises, fixed MLTS devices
  • January 6, 2022: Other MLTS devices (off-premises, non-fixed)

Source: FCC implementing rules (47 CFR Part 9), FCC fact sheets, 911.gov official guidance (verified October 2025)

1. Location Services Integration: Accurately determine and transmit the caller's location for effective emergency response. Implement multiple location detection methods (GPS, Wi-Fi, cellular triangulation) with fallback mechanisms to handle location failures. Provide dispatchable location information as mandated by RAY BAUM's Act, including street address, floor level, and room number for first responders.

   javascript

   class E911LocationService {
       async getDispatchableLocation() {
           try {
               const location = await this.getCurrentLocation();
               return this.formatDispatchableLocation(location);
           } catch (error) {
               this.handleLocationError(error);
               console.error("Error retrieving location:", error);
               return "Location unavailable";
           }
       }
   
       formatDispatchableLocation(location) {
           return `${location.address}, ${location.floor}, ${location.room}`;
       }
   
       handleLocationError(error) {
           // Log the error, attempt alternative location methods, or provide a default location
       }
   }
   
   // Example usage:
   const locationService = new E911LocationService();
   locationService.getDispatchableLocation().then(location => console.log(location));
   

2. MLTS Requirements Implementation: Implement Multi-Line Telephone Systems (MLTS) compliance with Kari's Law. Enable direct 911 dialing without prefixes and notify authorized personnel when a 911 call occurs. Include the caller's location in notifications to facilitate assistance.

   • Direct 911 Dialing: Enable users to dial 911 directly without any prefixes or access codes.
   • Personnel Notification System: Notify designated personnel (security, reception) when a 911 call is made. Include the caller's dispatchable location in the notification.
   • Location Information Transmission: Transmit accurate location data to the Public Safety Answering Point (PSAP).
   • Emergency Call Routing: Route 911 calls correctly to the appropriate PSAP.

graph TD
    A[911 Call Initiated] --> B{Direct Dialing Enabled?}
    B -- Yes --> C[Route Call to PSAP]
    B -- No --> D[Error Handler/Log Error]
    C --> E[Send Location Data]
    C --> F[Notify Personnel (with location)]
    E --> G[Confirm Delivery/Log Result]

Implement robust error handling and logging at each stage to ensure reliability.

Comprehensive Validation System

A robust validation system is essential for ensuring data integrity and preventing errors. Your system should validate the entire phone number, including the area code and exchange code, against known valid formats and restrictions.

class MissouriPhoneNumberValidator {
    constructor() {
        this.patterns = {
            general: /^\+1\s?(\d{3})\s?(\d{3})\s?(\d{4})$/, // Matches +1 followed by 10 digits
            tollFree: /^\+1\s?(800|888|877|866|855|844|833)\s?(\d{3})\s?(\d{4})$/ // Matches common toll-free prefixes
        };
    }

    sanitizeNumber(number) {
        return number.replace(/[^0-9+]/g, ''); // Removes all non-digit characters except +
    }

    extractExchangeCode(number) {
        return number.substring(2, 5); // Extracts the 3-digit exchange code
    }

    validateExchangeCode(code) { // Same function as before
        // ... (implementation from previous section)
    }

    checkFormat(number) {
        return this.patterns.general.test(number) || this.patterns.tollFree.test(number);
    }

    formatNumber(number) {
        const match = this.patterns.general.exec(number);
        if (match) {
            return `+1 (${match[1]}) ${match[2]}-${match[3]}`;
        }
        return number; // Return as is if no match
    }

    validate(number) {
        try {
            if (!number) {
                throw new Error('Phone number cannot be empty');
            }

            const cleanNumber = this.sanitizeNumber(number);
            const isValid = this.checkFormat(cleanNumber);

            if (isValid) {
                const exchangeCode = this.extractExchangeCode(cleanNumber);
                if (!this.validateExchangeCode(exchangeCode)) {
                    throw new Error('Invalid exchange code');
                }
            }

            return {
                isValid,
                number: cleanNumber,
                formatted: this.formatNumber(cleanNumber)
            };
        } catch (error) {
            return {
                isValid: false,
                error: error.message
            };
        }
    }
}

// Example usage:
const validator = new MissouriPhoneNumberValidator();
console.log(validator.validate("+1 (314) 555-1212")); // Valid
console.log(validator.validate("+15551212")); // Invalid format
console.log(validator.validate("+1 (800) 123-4567")); // Valid toll-free

This enhanced validation class provides you with a more robust solution for handling various phone number formats and potential errors. It includes sanitization, format checking, and specific exchange code validation.

Carrier Integration Best Practices

Integrating with carriers requires careful consideration of several factors:

1. Location Services: Implement redundant location detection methods (GPS, Wi-Fi, cellular triangulation) and fallback mechanisms. Support both device-based and network-based location acquisition. This redundancy is crucial for ensuring accurate location information, especially in challenging environments.

2. Number Portability: Number portability allows users to keep their phone numbers when switching carriers. Your system should support Number Portability Administration Center (NPAC) queries to determine the correct carrier for a given number. Implement Location Routing Number (LRN) routing to handle ported numbers correctly. Keep in mind that different types of ports have varying completion timeframes, ranging from 1 business day for simple wireless ports to 5+ business days for complex ports. You should be prepared to handle these varying timelines and potential delays.

3. Testing Framework: A comprehensive testing framework is essential for verifying the functionality and reliability of your carrier integration. Test various scenarios, including successful and failed calls, location accuracy, and number portability updates.

   javascript

   describe('Missouri Phone Number Validation', () => {
       const validator = new MissouriPhoneNumberValidator();
   
       test('validates correct area codes', () => {
           expect(validator.validate('+1 314 555 1234').isValid).toBe(true); // Valid Missouri area code
           expect(validator.validate('+1 999 555 1234').isValid).toBe(false); // Invalid area code
       });
   
       test('validates toll-free numbers', () => {
           expect(validator.validate('+1 800 555 1234').isValid).toBe(true); // Valid toll-free number
       });
   
       test('handles invalid exchange codes', () => {
           expect(validator.validate('+1 314 555 1234').isValid).toBe(true); // Valid exchange code
           expect(validator.validate('+1 314 111 1234').isValid).toBe(false); // Invalid N11 exchange code
           expect(validator.validate('+1 314 011 1234').isValid).toBe(false); // Invalid exchange code starting with 0 or 1
       });
   
       // Add more tests for edge cases and different scenarios
   });
   

This expanded testing framework provides a more comprehensive approach to validating your phone number handling logic. Remember to test various edge cases and error scenarios to ensure robustness.

Implementation Checklist

This checklist provides you with a quick reference for the key steps involved in implementing phone number handling in your applications:

• Basic number validation
• Exchange code restrictions
• Emergency services compliance (Kari's Law and RAY BAUM's Act)
• Location services integration (redundant methods and fallback mechanisms)
• Carrier integration setup (NPAC queries and LRN routing)
• Testing framework implementation (comprehensive scenarios and edge cases)
• Documentation updates

Understanding Missouri's Dialing Procedures

This section provides you with a detailed overview of Missouri's dialing procedures, including local, long-distance, and international calling requirements.

Modern Dialing Requirements

Missouri's dialing landscape has evolved significantly with the implementation of area code overlays and modern telecommunications systems. Understanding these changes is crucial for ensuring your applications handle dialing correctly.

Local Call Requirements

The introduction of area code overlays has transformed local calling procedures across Missouri. Overlays assign multiple area codes to the same geographic region, increasing the available number pool without requiring existing users to change their numbers. This has led to the following changes:

• Mandatory 10-Digit Dialing: All local calls in Missouri now require 10-digit dialing (area code + 7-digit number). Different regions transitioned at different times:
  • October 24, 2021: Area codes 417, 816, 314, and 660 transitioned to mandatory 10-digit dialing to support the 988 National Suicide Prevention Lifeline
  • February 24, 2024: Area code 573 transitioned to mandatory 10-digit dialing ahead of the 235 overlay implementation
  • 2024 Overlays: New overlays 235 (for 573), 557 (for 417), and 975 (for 816) reinforce the need for 10-digit dialing in their respective regions
• No "1" Prefix Required: For local calls, even with 10-digit dialing, you don't need to add "1" before the number.
• Emergency Services Unchanged: Dialing 911 and 988 remain 3-digit emergency numbers
• Grace Period Transitions: During overlay implementations, there's typically a permissive dialing period (often 30 days) where both 7-digit and 10-digit dialing are allowed. However, you should encourage users to adopt 10-digit dialing as soon as possible to ensure a smooth transition.

Sources: Missouri Public Service Commission official notices, FCC 988 implementation guidelines, Fox2Now coverage of 573/235 transition (verified October 2025)

Long-Distance and International Calling

For calls beyond your local area, the following formats apply:

• Domestic Long-Distance: Format: 1 + Area Code + 7-digit number. Example: 1-417-555-1234 (calling Springfield from St. Louis).
• International Calls: Outbound Format: 011 + Country Code + Number. Example: 011-44-20-7123-4567 (calling London from Missouri).

Number Portability Explained

Number portability allows consumers to keep their phone numbers when switching service providers. While this empowers consumers, it presents technical challenges for providers, which you must address in your implementations. The administration of the NANP, including number portability, has evolved over time, transitioning from AT&T to Bellcore, then to Lockheed Martin and Neustar, and finally to Somos, Inc. on January 1, 2019. Somos was awarded an eight-year contract in December 2020 (extending through 2028) to serve as the NANPA, Pooling Administrator, and Reassigned Numbers Database Administrator.

Source: FCC official announcements and Somos.com (verified October 2025)

Porting Timeline Requirements

Different types of ports have varying completion timeframes:

Source: FCC 47 CFR Part 52 Subpart C and wireless industry standards (verified October 2025)

Frequently Asked Questions

What area codes are used in Missouri?

Missouri uses 9 area codes: 314 (St. Louis metro), 816 (Kansas City metro), 417 (Southwest Missouri), 573 (Eastern Missouri), 636 (East-central Missouri), 660 (North-central Missouri), 235 (overlay for 573), 557 (overlay for 417), and 975 (overlay for 816). The 314 and 816 area codes are original NANP codes from 1947.

How do I validate a Missouri phone number in JavaScript?

Use the NANP format (+1 NXX-NXX-XXXX) where N is 2-9 and X is 0-9. Validate that the first digit of the exchange code is 2-9, block N11 patterns (211, 411, 911), and verify the area code matches one of Missouri's 9 valid codes. Implement regex patterns to check format and sanitize input before validation.

Is 10-digit dialing required in Missouri?

Yes, all Missouri area codes now require 10-digit dialing for local calls. Area codes 417, 816, 314, and 660 transitioned on October 24, 2021 (for 988 implementation), and area code 573 transitioned on February 24, 2024 (for 235 overlay). You do not need to dial "1" before the area code for local calls.

What are Kari's Law and RAY BAUM's Act requirements for E911?

Kari's Law (effective February 16, 2020) requires direct 911 dialing without prefixes in MLTS systems and mandates notification of on-site personnel. RAY BAUM's Act requires dispatchable location information (street address, floor, room number) be transmitted with 911 calls. Compliance deadlines were January 6, 2021 for on-premises fixed devices and January 6, 2022 for other MLTS devices.

How long does phone number porting take in Missouri?

Simple ports (wireless-to-wireless, wireline-to-wireless) take 1 business day per FCC rules. Wireless-to-wireless ports typically complete in ~2.5 hours based on industry standards. Complex ports involving multiple lines or special services may take multiple business days depending on validation requirements.

What is the NANP format for Missouri phone numbers?

The North American Numbering Plan (NANP) format is +1 (NXX) NXX-XXXX, where +1 is the country code, N represents any digit from 2-9, and X represents any digit from 0-9. This format applies to all Missouri phone numbers and ensures consistent formatting across North America and the Caribbean.